1. Field of the Invention
This invention relates to an apparatus for reproducing video signals recorded in many tracks formed on a record bearing medium and more particularly to an apparatus having a mode of reproducing the video signals at a high speed.
2. Description of the Related Art
In performing a high speed reproduction with a rotary-head type video signal reproducing apparatus such as a video tape recorder (hereinafter referred to as VTR), the reproducing head of the VTR scans the medium by straddling a plurality of recording tracks obliquely formed, as shown in FIG. 1(a) of the accompanying drawings, on a magnetic tape which is travelling at a high speed. Then, in cases where these tracks have guard bands provided between them or where adjacent tracks have signals obliquely azimuth recorded there at different azimuth angles, the envelope of a modulated video signal obtained from the reproducing head periodically have small signal parts as shown in FIGS. 1(b) and 1(c). In other words, the output level of the reproduced video signal becomes extremely low when the reproducing head scans either a part between adjacent tracks or a track having signals recorded at a different azimuth angle from the azimuth angle of the head.
In the conventional method for improving picture quality obtainable by high speed reproduction, two magnetic heads 10A and 10B having different azimuth angles from each other are disposed close to each other; and the output of each of these heads is arranged to be taken out only when the head is scanning a track which is of the same azimuth angle as the head. Pictures without any salient noise bars have been thus obtained by this method. FIG. 1(b) shows the envelope of the output of the head 10A and FIG. 1(c) that of the output of the other head 10B. With the output of the head 10A or the head 10B selectively produced in an apposite manner, a signal without any extremely low reproduction level part can be obtained as shown in FIG. 1(d).
In another method for improving the picture quality obtainable by high speed reproduction, the level of a modulated video signal reproduced from a recording tape is monitored; and data for a low level part of the reproduced signal is read out from a memory and is substituted for the low level part. That method also gives a picture without noise bars.
With the former method applied to the so-called two-head helical scanning type reproducing apparatus, however, the apparatus must have at least four heads. Besides, two heads must be arranged closed to each other. This results in a complex head arrangement. Further, the number of grooves of a rotary transmitter increases according as the number of heads increases to result in an increased size of the transmitter. This method is hardly practicable for an apparatus using a compact rotary head type drum, such as the so-called 8-mm VTR.
Meanwhile, the latter method necessitates use of a circuit for monitoring the reproduced level of the modulated video signal. However, the reproduction level of the video signal fluctuates due to changes in the relative positions of the magnetic tape and the head and inconsistencies of the head itself. Therefore, it is difficult to set apposite threshold levels for storing in the memory and for reading from the memory. Such setting is difficult particularly in terms of interchangeability.
Further, the conventional method of obtaining a noiseless reproduced picture by replacing a signal portion for which the reproduced signal is not obtainable in a normal state with information on a similar portion which is stored at the memory for a preceding field presents the following problem: During the process of change-over from writing into the memory to reading from the memory and vice versa, horizontal synchronizing signals obtained before and after the change over tend to deviate in phase from each other. This phase deviation then brings about a skew state. Especially, the skew increases in cases where the above stated high speed reproducing method is applied to the standard mode of an 8-mm VTR.